InputText: Fixed issue when activating a ReadOnly field when the underlying value is being modified. (#8242)

docs/CHANGELOG.txt

@@ -45,6 +45,8 @@ Other changes:
 
 - InputText: Fixed a bug where character replacements performed from a callback
   were not applied when pasting from clipbard. (#8229)
+- InputText: Fixed issue when activating a ReadOnly field when the underlying
+  value is being modified. (#8242)
 - Drags: Added ImGuiSliderFlags_NoSpeedTweaks flag to disable keyboard
   modifiers altering the tweak speed. Useful if you want to alter tweak speed
   yourself based on your own logic. (#8223)

imgui.h

@@ -29,7 +29,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM >= 12345')
 #define IMGUI_VERSION       "1.91.7 WIP"
-#define IMGUI_VERSION_NUM   19161
+#define IMGUI_VERSION_NUM   19162
 #define IMGUI_HAS_TABLE
 
 /*

imgui_widgets.cpp

@@ -4507,6 +4507,7 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
     const bool init_changed_specs = (state != NULL && state->Stb->single_line != !is_multiline); // state != NULL means its our state.
     const bool init_make_active = (user_clicked || user_scroll_finish || input_requested_by_nav);
     const bool init_state = (init_make_active || user_scroll_active);
+    bool readonly_swapped_text_data = false;
     if (init_reload_from_user_buf)
     {
         int new_len = (int)strlen(buf);
@@ -4537,14 +4538,17 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
         // Preserve cursor position and undo/redo stack if we come back to same widget
         // FIXME: Since we reworked this on 2022/06, may want to differentiate recycle_cursor vs recycle_undostate?
         bool recycle_state = (state->ID == id && !init_changed_specs);
-        if (recycle_state && (state->TextLen != buf_len || (strncmp(state->TextA.Data, buf, buf_len) != 0)))
+        if (recycle_state && (state->TextLen != buf_len || (state->TextA.Data == NULL || strncmp(state->TextA.Data, buf, buf_len) != 0)))
             recycle_state = false;
 
         // Start edition
         state->ID = id;
-        state->TextA.resize(buf_size + 1);          // we use +1 to make sure that .Data is always pointing to at least an empty string.
         state->TextLen = (int)strlen(buf);
+        if (!is_readonly)
+        {
+            state->TextA.resize(buf_size + 1); // we use +1 to make sure that .Data is always pointing to at least an empty string.
             memcpy(state->TextA.Data, buf, state->TextLen + 1);
+        }
 
         // Find initial scroll position for right alignment
         state->Scroll = ImVec2(0.0f, 0.0f);
@@ -4610,6 +4614,21 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
             state->Scroll.y = draw_window->Scroll.y;
     }
 
+    if (g.ActiveId == id && is_readonly)
+    {
+        // FIXME: Refresh buffer because cursor/selection code uses that data (see repro #8242)
+        // The "simple" way would be to copy buf into state->TextA, like in the block above.
+        // But because we like to live dangerously, we do a little swap....
+        // Removing the swap and only doing a TextA.clear() is a way to identify who's using TextA.Data.
+        state->TextLen = (int)strlen(buf);
+        state->TextA.clear();
+        state->TextA.Data = buf; // Ouch
+        state->TextA.Size = state->TextLen + 1;
+        readonly_swapped_text_data = true; // Need to always ensure that every code path below lead to this being handled
+        //state->TextA.resize(buf_size + 1);
+        //memcpy(state->TextA.Data, buf, state->TextLen + 1);
+    }
+
     // We have an edge case if ActiveId was set through another widget (e.g. widget being swapped), clear id immediately (don't wait until the end of the function)
     if (g.ActiveId == id && state == NULL)
         ClearActiveID();
@@ -5008,10 +5027,11 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
                     callback_data.UserData = callback_user_data;
 
                     // FIXME-OPT: Undo stack reconcile needs a backup of the data until we rework API, see #7925
-                    state->CallbackTextBackup.resize(state->TextLen + 1);
-                    memcpy(state->CallbackTextBackup.Data, state->TextA.Data, state->TextLen + 1);
-
                     char* callback_buf = is_readonly ? buf : state->TextA.Data;
+
+                    state->CallbackTextBackup.resize(state->TextLen + 1);
+                    memcpy(state->CallbackTextBackup.Data, callback_buf, state->TextLen + 1);
+
                     callback_data.EventKey = event_key;
                     callback_data.Buf = callback_buf;
                     callback_data.BufTextLen = state->TextLen;
@@ -5142,7 +5162,7 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
         // - Measure text height (for scrollbar)
         // We are attempting to do most of that in **one main pass** to minimize the computation cost (non-negligible for large amount of text) + 2nd pass for selection rendering (we could merge them by an extra refactoring effort)
         // FIXME: This should occur on buf_display but we'd need to maintain cursor/select_start/select_end for UTF-8.
-        const char* text_begin = state->TextA.Data;
+        const char* text_begin = buf_display;
         const char* text_end = text_begin + state->TextLen;
         ImVec2 cursor_offset, select_start_offset;
 
@@ -5304,6 +5324,13 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
     if (is_password && !is_displaying_hint)
         PopFont();
 
+    if (readonly_swapped_text_data)
+    {
+        IM_ASSERT(state->TextA.Data == buf);
+        state->TextA.Size = 0;
+        state->TextA.Data = NULL;
+    }
+
     if (is_multiline)
     {
         // For focus requests to work on our multiline we need to ensure our child ItemAdd() call specifies the ImGuiItemFlags_Inputable (see #4761, #7870)...